This invention relates to a method for stratified construction of a grass pitch such as a football ground, comprising a pitch cover in the form of an uppermost positioned growth layer and underlying layers containing draining mass, equipped with a draining system, and assigned an underground, air-based heating plant supplied heat energy thereto through a gaseous energy carrier such as air. Likewise, the invention relates to heatable grass pitches built stratifiedly up in accordance with the method and assigned a buried, underground heating plant.
The compulsory football season in this country (Norway) does not expire before late fall, and international matches extend the season still further. The need for usable grass grounds in springtime before the season starts, is large and, in the month of March, only a few grass grounds are satisfactory, even in the Southern parts of the country.
There exist heatable football fields, mainly based on buried electrical cables. Other underground heating plants comprise pipe systems for flowing hot water.
Through the heating of a grass pitch, snow and ice are efficiently melted, and permanent use of heating cables/hot water pipes through the winter season, frost may be kept away from the pitch area, so that frost heaving and the influence of the frost on the grass roots are avoided, especially in early spring months with hot days and cold nights. Underground heating systems could, possibly, be supplemented by covering tarpaulin in periods with heavy snow fall.
In connection with buried electrical cable systems for foot ball fields, etc., it presents a disadvantage that large amounts of superior energy are used. This alternative appears as particularly energy-requiring and unprofitable.
Using water-carried heat, one has certainly a larger energy flexibility. However, there exist risks for leakages and broken water pipes, complicating operation and maintenance.
Electrical heating cables as well as water pipes included in underground heating plants are relatively simple to lay and mount but, in the course of time, they will usually change positions, especially vertically, dependent on the nature of those masses in which they were laid and to what kind of treatment/load the surface layer/layers have been subjected at any time.
In heating cable plants as well as in water pipe plants, one has systematically avoided to use insulation layers beneath the heating cables/water pipes above the ground; the underlying layers of the field body being heated to no purpose.
Nor, known technique has been capable of securing even, stable surfaces of grass fields in the course of time.
The object of the invention has, therefore, been to overcome or reduce disadvantages of known technique and, thus, provide partly a rational method for building up and heating grass fields, partly a heatable grass field built up in accordance with the method and not exhibiting disadvantages, deficiencies or limitations of use and application, in or relating to known grass fields or to the buried heating plants thereof.
The object is realized through proceeding in accordance with the first method claim, respectively by means of a grass ground built stratifiedly up and assigned a buried heating plant based on air as heat energy carrier. Moreover, the grass pitch may be assigned a draining plant known per se and which, according to a special feature of the invention, may be utilized as an underground watering plant.
Use of air as heat energy carrier means versatile energy flexibility in respect of heating source/type. Solar energy, remote heat, heating pump, electricity, oil, gas, biofuel, wind force, etc. may be used.
Above a horizontal bottom layer, a draining mass layer is laid and rounded off absolutely accurately in respect of slope, preferably by means of laser technique, whereafter insulation is laid in the form of water-repellent material practically insensitive to influence from the immediately adjacent layers. The insulation may consist of relatively rigid, shape-durable plate units joined together to form large flake-like coverings or coats.
Above the insulations which has the task of preventing energy in supplied heated air to escape in a direction downwardly into the ground, follow two horizontal parallel cavities which, except from fluid communication along the outer edges of the pitch, are separated from each other and serve as air-conveying cavities. The simplest way of forming the cavities is between parallel, horizontal plates, spacers being placed in the cavities.
According to the preferred embodiments of the invention, the three parallel, horizontal plates are formed as corrugated plates of e.g. steel, which gives a strong structure in which the xe2x80x9cspacersxe2x80x9d are built into the plate design. The intermediate corrugated plate layer is provided with a number of vertical, through-going holes which, preferably, are distributed along the outer edges and constitute fluid communication between the lower and upper cavities. Heated air blown into the cavity formed by the two lowermost corrugated plate layers disperses itself across the respective cavity""s area (corresponding to the area of the grass pitch), in order to, through said through-going holes in the central corrugated plate layer, to flow up into the upper cavity, from where the air can be sucked out of the upper cavity for, thereafter, to be heated up once more within a suitable heating device.
Dependent on the size and extent of the grass pitch in width and length, several such circuits for air as energy carrier may be disposed.
The three corrugated plate layers are placed such in relation to each other that lower and upper layer""s rectilinear crests of the waves extend mutually parallel, while the intermediate corrugated plate layer""s crest of waves cross the crests of waves of the two adjacent layers perpendicularly.
Above the uppermost corrugated plate layer, a concrete layer has been cast and in which expansion joints are inserted with appropriate spacings and equidistantly distributed across the area of the entire grass pitch. The concrete layer is load-bearing and secures a non-changeable, horizontal support layer.
The work with the building of the pitch is continued on top of the concrete layer through the positioning of an in per se known draining pipe system which, in accordance with the invention, is disposed such that it, besides its well known draining function, may carry out watering and venting from within the upper layer of the pitch-bed, Around the draining pipes, a so-called xe2x80x9cgardener""s feltxe2x80x9d can be disposed, the felt being temporarily coiled together so that adjacent draining masses ay be packed well together within the chosen layer thickness. Thereafter, gardener""s felt is stretched out upon the top of the draining masses. Immediately on top of the gardener""s felt, a so-called building cloth may be placed before the uppermost layer, the growth layer, is positioned. The air-conducting pipes of the heating plant are laid during the building of the grass pitch and secure that heated air becomes conducted into the lowermost cavity at a larger number of air supply spaces distributed across the area of the entire pitch, where an upright, upwardly open branch pipe supplies heated air forcedly (by means of a fan) to the lower cavity which is filled with this heated air within its entire volume, so that the pitch is heated across its entire area, until the air blown in, in a cooler condition, reaches the edge perforations in the intermediate corrugated plate and, through these, ends in the upper cavity where only a suction out of the air takes place, in order to, thereafter, heat it up again by means of a heating aggregate which can be disposed within a covered culvert which, e.g., extends through the entire pitch body.